A difficult obstacle associated with the exploration and production of oil and gas is management of significant ocean currents. These currents can produce vortex-induced vibration (VIV) and/or large deflections of tubulars associated with drilling and production. VIV can cause substantial fatigue damage to the tubular or cause suspension of drilling due to increased deflections. While helical strakes, if properly designed, can reduce the VIV fatigue damage rate of a tubular in an ocean current, they typically produce an increase in the drag on the tubular and hence an increase in deflection. Thus, helical strakes can be effective for solving the vibration problem at the expense of worsening the drag and deflection problem.
A better solution is to use fairings as the VIV suppression device. A properly designed fairing can reduce both the VIV and the drag. A problem associated with fairings on drilling risers has been the cost of installation and retrieval of the fairings. If the fairings are excessively large, then handling difficulties can produce long installation times. Sometimes, the economics are such that running the riser without fairings has a higher expected return value than installing the fairings due to these high installation costs.
Tail fairings are suppression devices that produce reduction in both VIV and drag, but are lighter and faster to install than traditional full fairings. These fairings consist of only the tail portion of a fairing together with straps at each end to hold the tail to the tubular.
Tail fairings, while faster to install than traditional full fairings, can be difficult to install when the brackets and straps do not line up correctly. In addition, tail fairings cannot be used for multiple sized risers, and must be used only for the buoyancy size for which they were designed. Tail fairings also typically require at least one collar per fairing to keep them from sliding down the tubular.